@ jd100
POP stands for Post Office Protocol. It is a protocol that mail programs use to download mail from a POP mail server. When you’re using this and you did not leave a copy of the messages to the server. All emails transferred from the server to your computer will no longer appear on the web interface and there’s no way for us to retrieve it.
For assistance on how to enable the leave a copy of the messages to the server, I suggest that you contact the support group of your email client.